Weather woes

If a weakening, slowing polar jet stream is causing weather patterns to stall, leading to extreme weather (7 July, p 32), imagine the disruption if it were to disappear altogether.

Jet streams – high-speed winds in the upper atmosphere – occur at the meeting point of atmospheric “cells”, large-scale circulations of air, such as that created by air rising at the equator and flowing polewards before sinking in the subtropics. In each hemisphere, the polar jet stream occurs between two cells, the polar cell and the mid-latitude Ferrel cell, and helps guide weather systems.